The present invention relates to a polymer film laminate and, in particular, to such a laminate which is opaque and which possesses at least one major surface capable of absorbing liquid media.
Cellulosic papers and other types of fibrous webs, including the woven and non-woven varieties, fabricated from non-cellulosic polymeric materials such as the polyolefins, polyamides, polyesters, and the like, are currently the materials of choice for the manufacture of a wide range of products requiring relatively strong but inexpensive sheet material which has the ability to absorb liquid media such as inks, water based adhesives, oils, etc. Such materials find use as label stock, envelopes, especially courier envelopes, oil-filled electrical capacitors as well as numerous other applications.
Extruded polymer films whether of the mono-layer or multi-layer (i.e., laminate) type have received little attention as materials for the construction of such products due primarily to the non-absorbent character of their surfaces. While resin films can be made to exhibit exceptional strength and at a cost which is competitive with paper and other types of fibrous sheet materials, their inability to absorb liquid media such as those aforementioned precludes their use in the manufacture of products where liquid absorbency is an essential functional requirement.
U.S. Pat. No. 4,377,616, the contents of which are incorporated by reference herein, discloses an opaque biaxially oriented polymer film structure comprising a thermoplastic polymer matrix core layer possessing numerous voids, a substantial number of which contain at least one spherical void-initiating particle, and transparent thermoplastic skin layers adhering to both major surfaces of the core layer. The unique structure of the core layer imparts a much higher degree of opacity, possibly due to the effects of light scattering, than that possible by the use of opaquing pigment alone. However, in this arrangement, the application of skin layers which are essentially non-absorbent to both major surfaces of the core layer which, due to the presence of numerous voids therein, exhibits absorbency for liquid media, prevents the absorbent capability of the core layer from being effectively utilized or exploited